How many Farad is enough in the bridge rectifier ?

How many Farad is enough in the bridge rectifier ?

I see some people use over 10000uF in tube pre-amp  ](*,)  [-X
(PS : that tube pre-amp only charge 20W RMS power from AC mains)

So, how many Farad (uF) is enough ?

How to calculate?

KK.HO

See below :

o Minimum input voltage on top of the transformer: this is the peak    rectified minimum AC input voltage minus the peak-peak ripple voltage

See the simple equation

f line means freq of the AC mains, which is 50Hz in HK;
Correct

P o-max is the max power required in the pre;
Correct

V DC-min is the VDC that the loading needs;
Min operating voltage of the device.

but what is V AC-min??[/quote]
Your transformer should have diff on no-load and full load, under the full load, the AC output from the transformer will drop.
Or you can use 5-10% on it.

Basically, I am using high power DC supply as source to the device, and monitoring the current using Current probe with OSC. (not digit reading type, it cannot show the transient response!!!)

Therefore, I can easily to find the "min" capacitor value that for the device.

KK.